Power management system for a mobile station

ABSTRACT

A power management system for a mobile station reduces standby mode processing by receiving and processing single time slots of a short paging channel. Each single time slot of a short paging channel includes a mobile station identifier which alerts a receiving mobile station that a pending telephone call or paging message may be directed to the mobile station. Once so alerted, the mobile station receives and processes full paging channels comprising four time slots to determine whether the mobile station is the intended recipient of the telephone call or paging message. If the mobile station determines that it is not the intended recipient, then the mobile station resumes receiving and processing single time slots of the short page channel. Processing fewer time slots of data for purposes of call detection conserves mobile station battery power.

This application is a continuation of Ser. No. 08/959,588 filed Oct. 29,1997 now U.S. Pat. No. 6,044,069.

BACKGROUND

This invention relates to the field of wireless communication systems.More specifically, the present invention relates to a power managementsystem for mobile stations.

The use of wireless communication systems is growing every day withusers now numbering well into the millions. Mobile stations, such ashandheld telephones, are becoming more portable and easier to use allthe time, and mobile station users now rely daily on the availability ofwireless systems to accommodate their communication needs. However, thesingle greatest inconvenience associated with routine use of a mobilestation is the constant need to recharge and replace worn downbatteries. Even users who make and receive very few telephone calls andoperate their mobile stations mostly in the standby mode (awaitingcalls) experience the annoying and frequent problem of the mobilestation running out of battery power thus becoming dead and uselessuntil the worn battery is replaced with a charged battery. Users demandmobile stations having the longest possible battery life.

A large portion of battery power consumed in standby mode isattributable to call detection processing. For example, in GSM-basedwireless communication networks, about once every second a mobilestation receives and decodes a full paging message comprising fourgroups of digital data transmitted at certain time intervals to detectany calls. Only rarely does the detection attempt result in discovery ofa telephone call for the mobile station. A great deal of battery poweris consumed in this call detection process.

Also, while in standby mode, a mobile station periodically receives andprocesses transmitted broadcast control data including information aboutcommunication parameters (channels, frequencies, communication options,etc.). Existing mobile stations receive and process broadcast controldata frequently and without fail, for example every 30 seconds,regardless of whether the information contains anything useful to themobile station. Again, battery power is consumed by this processing evenwhere the mobile station obtains no new information.

Battery power is even consumed when the mobile station is performing noreceiving and processing whatsoever. This is because existing mobilestations use a very high precision master clock that runs continuously.Such master clocks are extremely precise and permit the mobile stationsto engage in precisely timed communication as required by many wirelesscommunications standards, and particularly by those such as GSM whichdepend on time division multiple access wherein mobile stations areallocated very short time periods within which to communicate. The highprecision of master clocks comes at a price, however, as such masterclocks consume battery power at a much higher rate than clocks havinglower precision.

Improvements in battery technology, while helpful, have done little toavoid the seemingly ever-present need to recharge and replace mobilestation batteries. What is needed is a system to conserve battery powerby minimizing mobile system processing, particularly in standby mode.

SUMMARY

The present invention is directed to reducing power consumed by a mobilestation operating in standby mode. The present information reduces thequantity of data that the mobile station receives and processes todetect pending telephone calls or paging messages. The reducedprocessing consumes, less power and advantageously increases the standbymode lifetime of a mobile station battery. Moreover, the presentinvention reduces the frequency with which the mobile station receivesand processes broadcast control information while preserving the abilityof the mobile station to detect and process any updated information in abroadcast control channel. Processing fewer broadcast control channelsalso has the advantage of increasing the lifetime of a mobile stationbattery. Further, the invention reduces the power consumed by the mobilestation when completely idle (i.e., when the mobile station is notreceiving, transmitting, or processing any data), still furtherincreasing the lifetime of a mobile station battery.

In one embodiment of the present invention, a mobile station comprises:(1) a software instruction processing unit; (2) a software instructionstorage comprising a computer-readable medium, the software instructionstorage accessible to the software instruction processing unit; (3) ashort page channel receiving module stored in the software instructionstorage, the short page channel receiving module including receivinginstructions executed by the software instruction processing unit, thereceiving instructions causing the mobile station to scan broadcastinformation in a wireless communication network for a short page channeland to receive a single time slot of the short page channel containingone group of call alert data; and (4) a short page processing modulestored in the software instruction storage, including processinginstructions executed by the software instruction processing unit, theprocessing instructions causing the mobile station to process the onegroup of call alert data and to determine from the group of call alertdata whether a pending telephone call or paging message may have beendirected to the mobile station. A preferred aspect of the mobile stationfurther comprises: (1) an idle state wherein the mobile station does notscan for a short page channel or receive or process call alertinformation, the mobile station entering the idle state during a timeperiod between broadcasts of the short page channel; and (2) a batteryproviding power to the mobile station, the mobile station consuming thepower at a first rate during the scanning for the short page channel andduring receiving or processing the call alert information, the mobilestation consuming the power at a second rate in the idle state, thesecond rate being less than the first rate. A further preferred aspectof the mobile station further comprises: (1) a master clock; and (2) alow precision clock, the low precision clock being sufficiently preciseto time the receipt of a single short page channel time slot, the lowprecision clock less precise than the master clock, the low precisionclock consuming less power during a time interval than the master clock,the low precision clock timing the idle state, the master clock shutdown during the idle state.

In another embodiment, a mobile station comprises: (1) a call alertmodule structured to extract an alert message from transmitted callalert data, the call alert module responding to call alert data receivedfrom a call alert channel of a wireless communication system by alertingthe mobile station of a pending telephone call or paging message whichmay be directed to the mobile station; and (2) a paging modulestructured to extract a paging message from transmitted paging data, thepaging module responding to paging data received from a paging channelof the wireless communication system by determining whether thetelephone call or paging message is directed to the mobile station, thealert data requiring less processing than the paging data. A preferredaspect of the mobile station further comprises a call establishmentmodule which initiates the establishment of a communication link to acommunication device responsible for initiating the telephone call orpaging message, the call establishment module invoked upon thedetermining that the telephone call or paging message is directed to themobile station.

In a further embodiment of the present invention, a cellular systemcomprises: (1) a base station; (2) a cell; (3) a receiver in the cell;(4) an alert channel in which the base station transmits within the cellalert information to alert the receiver of a pending telephone call orpaging message; and (5) a paging channel in which the base stationtransmits within the cell paging information to notify a receiver thatthe receiver is the intended recipient of said telephone call or pagingmessage, the paging information requiring less processing by thereceiver than the alert information. In a preferred aspect, the cellularsystem further comprises receiver identity information within the alertinformation, the receiver identity information not uniquely identifyingthe receiver.

In still another embodiment of the present invention, a mobile station,with reduced standby processing requirements, comprises: (1) a datastorage area; (2) a paging group value stored in the data storage area,the paging group value specifying first paging channels, the paginggroup value assigned to the mobile station by a mobile switching center;and (3) a paging channel skipping value stored in the data storage area,the paging channel skipping value specifying a subset of the firstpaging channels, the subset identifying paging channels transmitted lessfrequently than said first paging channels, the mobile station receivingand processing the subset of the first paging channels.

In a still further embodiment of the present invention, a short pagechannel time slot is stored in a computer-readable medium. The shortpage channel comprises: (1) mobile station identity information fromwhich a mobile station receiving the short page channel time slot aspart of a broadcast TDMA frame determines that a pending telephone callor paging message may have been directed to the mobile station; and (2)error detection information from which a mobile station receiving theerror detection information along with the mobile station identityinformation in the short page channel time slot determines whether datareceived in the short page channel time slot contains errors.

In another embodiment of the present invention, a mobile switchingcenter comprises: (1) a data storage area, the data storage areacontaining a mobile station identifier value associated with a mobilestation; and (2) a short page channel creation module invoked by themobile switching center upon detection by the mobile switching centerthat a telephone call is being directed to the mobile station, the shortpage channel creation module combining in a single time slot of a TDMAframe the mobile station identifier value and error detection data, themobile switching center including the single time slot of the TDMA framewithin a multiframe for transmission to a base station. In a preferredaspect, the mobile switching center further comprises a bit for updatingbroadcast control information, the bit combined in the single time slot,the bit having a first value if the content of the most recentlytransmitted broadcast control channel in a particular cell did notchange from the content of an inmmediately preceding broadcast controlchannel transmitted to the same cell, the bit having a second value ifthe content of the recently transmitted broadcast control channel isdifferent from the content of the immediately preceding broadcastcontrol channel.

In yet another embodiment of the present invention, a mobile station,with reduced requirements for processing broadcast control data,comprises: (1) a data storage area; (2) a short page channel data bufferin the data storage area including a bit reserved for updating broadcastcontrol information, the bit received by the mobile station from a timeslot of a TDMA frame; (3) a software instruction storage in acomputer-readable medium; (4) a broadcast control update module storedin the software instruction storage, the broadcast control update moduleresponding to receipt of the bit by comparing the bit to a priorreceived bit stored in the data storage area and, if the compared bitsdiffer, directing the mobile station to receive and process a nexttransmitted broadcast control channel to update communication parametersof the mobile station, otherwise if the compared bits are the same,storing the newly received bit in place of the prior received bit.

In another embodiment of the present invention, a mobile stationcomprises: (1) a master clock; and (2) a low precision clock, the lowprecision clock consuming less power than the master clock, the lowprecision clock used to time an idle state wherein the mobile station isnot receiving, transmitting, or processing data, the master clock shutdown during the idle state.

In still another embodiment of the present invention, a wirelesscommunication system comprises: (1) a mobile switching center, themobile switching center generating a first single time slot of a shortpage channel, the first single time slot including a first mobilestation identifier value, the mobile switching center transmitting thefirst single time slot to a base station, the mobile switching centergenerating a paging channel having four time slots, the four time slotsincluding a second mobile station identifier, the mobile switchingcenter transmitting the four time slots to the base station; (2) a basestation which receives the first single time slot and the four timeslots, the base station transmitting to a cell the first single timeslot in a short page channel and the four time slots in a pagingchannel; and (3) a mobile station in the cell, the mobile stationidentified by the first mobile station identifier and by the secondmobile station identifier, the mobile station receiving the first singletime slot from the short page channel and extracting the first mobilestation identifier from the first single time slot to determine that apending telephone call or paging message may be directed to the mobilestation, the mobile station, upon the determination, receiving the fourtime slots from the paging channel and extracting the second mobilestation identifier to conclude that the mobile station is the intendedrecipient of the telephone call or paging message, the mobile station,upon the conclusion, initiating call establishment procedures to createa communication link between the mobile station and a communicationdevice responsible for initiating the telephone call or paging message.In a preferred aspect, wireless communication system comprises abroadcast control update bit, the update bit included in the firstsingle time slot, the update bit having a first value if the content ofa most recently transmitted broadcast control channel in the cell didnot change from the content of an immediately preceding broadcastcontrol channel transmitted to the cell, the bit having a second valueif the content of the recently transmitted broadcast control channel isdifferent from the content of the immediately preceding broadcastcontrol channel, the mobile station extracting the update bit from thefirst single time slot and, if the update bit has the second value, thenthe mobile station receiving and processing a next transmitted broadcastcontrol channel. In another preferred aspect, the wireless communicationsystem comprises: (1) a data storage area in the mobile station; (2) apaging group value stored in the data storage area, the paging groupvalue specifying first paging channels, the paging group value assignedto the mobile station by the mobile switching center; and (3) a pagingchannel skipping value stored in the data storage area, the pagingchannel skipping value specifying a subset of the first paging channels,the subset including a number of paging channels fewer than the numberof paging channels comprising the first paging channels, the mobilestation receiving and processing the subset of the first pagingchannels. In another preferred aspect, the wireless communication systemfurther comprises: (1) a master clock timing the receipt of the fourtime slots by the mobile station; (2) a second single time slot, themobile switching center transmitting the second single time slot to thebase station, the base station transmitting to the cell the secondsingle time slot in the short page channel, the mobile station receivingthe second single time slot from the short page channel upon determiningfrom the receipt of the first single time slot that a pending telephonecall or paging message is not directed to the mobile station; and (3) alow precision clock timing the duration of an idle state wherein themobile station does not receive, transmit, or process data, the durationof the idle state occurring after the receipt by the mobile station ofthe first single time slot and before the receipt by the mobile stationof the second single time slot, the second single time slot containingsufficient synchronization bits to permit the receipt of the secondsingle time slot, the master clock shut down during the idle state, thelow precision clock consuming less power during a time interval than themaster clock.

These and other embodiments are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates components of a wireless communication system;

FIG. 2 illustrates wireless communication signal data transmitted by abase station and structured in data frames;

FIG. 3 illustrates a mapping of bits in a single paging channel (PCH)time slot;

FIG. 4 illustrates a mapping of 456 coded bits comprising a pagingchannel;

FIG. 5 illustrates a multiframe in accordance with an embodiment of thepresent invention;

FIG. 6 illustrates a mapping of bits in one embodiment of a short pagechannel (SPCH) time slot;

FIG. 7 illustrates components of a mobile switching center in accordancewith an embodiment of the present invention;

FIG. 8 illustrates components of a mobile station in accordance with anembodiment of the present invention;

FIG. 9 illustrates steps performed by a mobile station to register witha mobile switching center in accordance with an embodiment of thepresent invention;

FIG. 10 illustrates steps performed by a mobile station and a mobileswitching center to register and activate the mobile station in a cellin accordance with an embodiment of the present invention;

FIG. 11 illustrates steps performed to scan a base station transmissionfor telephone calls or page messages in accordance with an embodiment ofthe present invention;

FIG. 12 illustrates steps performed to determine whether a mobilestation is the target of a pending telephone call or page message inaccordance with an embodiment of the present invention;

FIGS. 13A and 13B illustrate steps performed by the mobile switchingcenter to generate a short page channel (SPCH) in accordance with anembodiment of the present invention;

FIG. 14 illustrates steps performed by a mobile station to time an idlestate using a low precision clock in accordance with an embodiment ofthe present invention; and

FIG. 15 illustrates two sequences of multiframes, one sequence beingused by existing GSM-based systems having no short page channels SPCHand another sequence in accordance with a preferred embodiment of thepresent invention using short page channels 504 SPCH.

DETAILED DESCRIPTION

FIG. 1 illustrates components of a wireless communication system. Amobile switching center (MSC) 102 communicates with a base station (BS)104. The base station 104 broadcasts data to and receives data frommobile stations 106 within a cell 108. The cell 108 is a geographicregion, roughly hexagonal, having a radius of up to 35 kilometers orpossibly more.

A mobile station 106 is capable of receiving data from and transmittingdata to a base station 104 in compliance with GSM (global system formobile communications). GSM is a communication standard permittingmobile users of wireless communication devices to exchange data over atelephone system wherein radio signals carry data to and from thewireless devices.

Under the GSM standard, additional cells adjacent to the cell 108 permitmobile stations 106 to cross cell boundaries without interruptingcommunications. This is so because base stations in adjacent cellsassume the task of transmitting and receiving data for the mobilestation 106. The mobile switching center 102 coordinates allcommunication to and from mobile stations in a multi-cell region, thusthe mobile switching center 102 may communicate with many base stations.

Mobile stations 106 may move about freely within the cell 108 whilecommunicating either voice or data to other, perhaps fixed, telephoneusers. Mobile stations not in active communication with other telephonesystem users may, nevertheless, scan base station 104 transmissions inthe cell 108 to detect any telephone calls or pages directed to themobile station 106.

One example of such a mobile station 106 is a cellular telephone used bya pedestrian who, expecting a telephone call, powers on the cellulartelephone while walking in the cell 108. The cellular telephone scanscertain frequencies (frequencies known to be used by GSM) to synchronizecommunication with the base station 104. The cellular telephone thenregisters with the mobile switching center 102 to make itself known asan active user within the GSM network. The cellular telephone scans dataframes broadcast by the base station 104 to detect any telephone callsor pages directed to the cellular telephone. In this call detectionmode, the cellular telephone receives, stores and examines pagingchannel data, and determines whether the data contain a mobile stationidentifier matching an identifier of the cellular telephone. If a matchis detected, the cellular telephone engages in a call establishmentconversation with the mobile switching center 102 via the base station104. If no match is detected, the cellular telephone enters an idlestate for a predetermined period of time, then exits the idle state toreceive another transmission of paging channel data.

The receiving and processing of paging channel information to detecttelephone calls and page messages consumes power. Millions of consumersuse mobile stations 106, such as portable, hand held cellulartelephones, that rely on batteries for power. Consumers routinely carrytwo, three and sometimes more cellular telephone batteries due to therelatively short life of the charge in one battery. Even consumers whoinitiate and receive relatively few telephone calls on their cellulartelephones must frequently recharge and replace batteries because of thepower consumed by the cellular telephone while in standby operation(waiting for an incoming call).

The present invention substantially reduces the power consumed by acellular telephone (or other mobile station) to detect telephone callsor paging messages and consequently increases battery lifetime. Toreduce power consumption, the present invention provides a short pagemessage (or call alert message) containing one-fourth the data ofexisting paging (call detection) messages. A mobile station thusreceives and processes the short page message to detect telephone callsand page messages, rather than receiving and processing the existing,much longer paging messages. The short page message alerts the mobilestation 106 that there may be a telephone call or paging messagedirected to the mobile station, in which case it then looks for andprocesses a longer paging message. The invention substantially reducescall detection processing and increases the amount of idle time betweencall detection processing, thus substantially extending the lifetime ofa single battery charge.

A common implementation of the GSM system uses frequencies in the900-MHz range. In particular, mobile stations 106 transmit in the890-915-MHz range and base stations 104 transmit in the higher935-960-MHz range. Each 25-MHz range is divided into 125 radio frequencychannels, each having a width of 200 kHz. The direction of communicationfrom a mobile station 106 to a base station 104 is referred to asuplink, and the direction from a base station 104 to a mobile station106 is referred to as downlink.

FIG. 2 illustrates wireless communication signal data transmitted by abase station 104 and structured in data frames, sometimes calledtime-division multiple access (TDMA) frames, according to the GSMstandard. The GSM specification provides eight time slots (or physicalchannels) in each 200 kHz radio channel. An entire data frame has aduration of 4.615 milliseconds. Each time slot has a time length of 577microseconds (4,615/8=577). Because a mobile station 106 may use onlyone time slot in any data frame, it must transmit any information within577 microseconds.

As shown in FIG. 2, a data frame 202 has eight time slots 204 (orphysical channels). The time slots 204 carry bit-oriented controlinformation, voice information, or data. Generally, the first time slotof each frame 206 holds bit-oriented control information. Controlinformation is used in a GSM-based system to broadcast synchronizationinformation and system parameters and options, to notify mobile stations106 of pending telephone calls or page messages, and to grant mobilestations 106 access to other physical channels.

The time slots carrying control information are formatted in groups of51 time slots (i.e., the first time slot of each of 51 successiveframes) referred to as a multiframe 208. Downlink informationtransmitted to a mobile station 106 by a base station 104 is formattedin multiframes 208. In accordance with the GSM standard, a multiframe208 may include four types of control information: (1) a frequencycorrection channel 210 (FCCH) which provides the mobile station 106 withthe frequency reference of the GSM system; (2) a synchronization channel212 (SCH) which supplies the mobile station with the key (or trainingsequence) it needs to be able to demodulate the information coming fromthe base station 104 and also contains a frame number, as well as thebase transceiver station identity code (BSIC); (3) a broadcast controlchannel 214 (BCCH) which informs the mobile station 106 about specificsystem parameters it may need to identify the network or to gain accessto the network (e.g., location area code, operator identification,information on which frequencies the neighboring cells may be found,different cell options, and access other parameters); and (4) a commoncontrol channel 216 (CCCH) which supports the establishment of a linkbetween a mobile station 106 and a base station 104.

A common control channel 216 CCCH may have different uses. A commoncontrol channel 216 may be a paging channel 218 (PCH), which providesinformation indicating whether a telephone call or paging message iscurrently pending for a particular mobile station 106. A common controlchannel 216 may also be an access grant channel (AGCH) through which amobile station 106 acquires information identifying another channel touse for its communication needs.

The frequency correction channel 210 FCCH and the synchronizationchannel 212 SCH each consist of bit-oriented data in a single time slot.The broadcast control channel 214 BCCH, however, as well as the commoncontrol channel 216 CCCH each use four time slots to carry information.In particular, a common control channel 216 CCCH used as a pagingchannel 218 PCH uses four time slots of bit-oriented data 220, each timeslot carrying 156.25 bits.

FIG. 3 illustrates a mapping of bits in a single paging channel (PCH)time slot. As provided in the GSM specification, bits in a pagingchannel PCH time slot may be allocated as follows: Three tail bits 302,followed by 57 coded bits 304, followed by one flag bit 306, followed by26 training sequence bits 308, followed by one flag bit 310, followed by57 coded bits 312, followed by three tail bits 316, and terminated by an8.25-bit guard period 318. Those of ordinary skill in the art mayrecognize this bit mapping as a normal burst. The guard periodrepresents a period of time, approximately 30.4 microseconds, duringwhich a mobile station ramps up RF power, and no information is conveyedby the guard period. The tail bits 302, 316 are also used to provideguard time and facilitate additional time for RF power ramping. The flagbits 306, 310 and the training sequence bits 308 contain no actualpaging channel information, and instead are used for synchronization.

The paging channel information is contained in the first 57 coded bits304 and the second 57 coded bits 312 which combine to form 114 codedbits 320. Thus, there are 114 coded bits representing paging channelinformation in each time slot of a paging channel (PCH). As FIG. 2illustrates, the four time slots of a paging channel carry four groupsof 114 coded bits, resulting in a total of 456 coded bits per pagingchannel (PCH).

FIG. 4 illustrates the mapping of the 456 coded bits carried by eachpaging channel. Those of ordinary skill in the art will appreciate thatthe 456 coded bits of the paging channel are interleaved 402. Generally,bit-oriented data may be interleaved to assist in detection andcorrection of transmission-related errors in received bit-oriented data.The interleaving of bit-oriented data is well known but complicated andis not discussed in detail herein. See Siegmund M. Redl, et al., AnIntroduction to GSM, 123 (1995) for more details. Meaningful informationcannot be extracted from interleaved data, such as the 456 interleavedcoded bits, until they are reordered. Because of the nature of theinterleaving, it will be appreciated that the 456 interleaved coded bitscannot be reordered until all of the 456 interleaved coded bits havebeen received and stored by a mobile station 106.

Under the GSM standard, a mobile station 106 typically receives fourtime slots of bit-oriented data in a paging channel PCH, comprising atotal of 625 bits (4*156.25=625). Using known techniques, the mobilestation 106: (1) eliminates the tail bits 302, 316, the flag bits 306,310, the training sequence bits 308, and the guard period bits 318 fromthe bits of each time slot to isolate the 456 interleaved coded bits402; (2) reorders the 456 interleaved coded bits yielding a bit streamcomprising 456 coded bits 404; and (3) decodes the 456 coded bits toreverse the convolutional coding performed prior to transmission of thepaging channel information to derive 228 bits 406.

The decoded 228 bits include 40 parity bits 408 to verify that thepaging information has been received correctly and four zero bits 410 toreset a decoder. The mobile station 106 accesses paging information 412contained in 184 bits. In particular, a mobile station 106 accesseseither a first 64-bit mobile identity value 414 or a second 64-bitmobile identity value 416 (it is predetermined whether the mobilestation will examine the first or second mobile identity) to determinewhether a telephone call or paging message was directed to the mobilestation 106. The mobile station 106 determines a telephone call orpaging message was directed to the mobile station 106 by comparing theaccessed mobile identity value to an internally stored identificationcode. Thus, under GSM specifications, when the mobile identity value414, 416 matches the internally stored identification code, the mobilestation 106 determines that a telephone call or paging message wasdirected to the mobile station 106.

FIG. 5 illustrates a multiframe 502 in accordance with one embodiment ofthe present invention. In addition to carrying frequency correctionchannels 210 (FCCH), synchronization channels 212 (SCH), broadcastcontrol channels 214 (BCCH), and common control channels 216 (CCCH), themultiframe 502 includes a short page channel 504 (SPCH). In oneembodiment of the present invention, the short page channel 504 (SPCH)includes four time slots 506. Each time slot 506 of the short pagechannel (SPCH) contains information sufficient to alert at least onemobile station 106 that there may be a telephone call or paging messagedirected to the mobile station 106. Each time slot 506 of the short pagechannel 504 contains 156.25 bits.

In another embodiment of the present invention, the short page channel504 SPCH is implemented as another type of common control channel 216CCCH. Thus, in that embodiment, any common control channel 216 CCCHcould be allocated as one of the following: a paging channel 218 PCH, anaccess grant channel AGCH, or a short page channel 504 SPCH.

FIG. 6 illustrates the mapping of bits in one embodiment of a short pagechannel (SPCH) time slot. A mobile station 106 monitoring a time slot506 of the short page channel 504 receives three tail bits 602, 39 codedbits 604, 64 synchronization sequence bits 606, 39 coded bits 608, threetail bits 610, and a guard period region 612 of 8.25 bits. Those ofordinary skill in the art may recognize that a synchronization burstformat is being used. While alternative embodiments of the presentinvention operate using different time slot formats, the synchronizationburst format reduces the timing precision required to receive a shortpage channel time slot 506. The reduced timing precision requirementsare exploited to reduce power consumption, as is explained in moredetail further below.

In accordance with the present invention, a single time slot 506 of theshort page channel 504 alerts a mobile station 106 of a possible pendingtelephone call or paging message. Thus, there is no need for a mobilestation 106 to receive multiple time slots of a short page channel SPCHand thus no need to detect or correct bit transmission errors overmultiple time slots. Accordingly, the bits of each short page channeltime slot need not be interleaved with bits of other time slots, inwhich case a mobile station 106 need perform no reordering of receivedbits of a short page channel time slot. In another embodiment of thepresent invention, the 78 bits in a short page channel time slot may beinterleaved according to well known interleaving schemes to facilitatedetection and correction of bit transmission errors affecting the bitsin a time slot.

Regardless of whether the bits are interleaved, the mobile station 106need not wait to receive any additional time slots. Rather, as discussedbelow, the mobile station 106 may process the bit data in a single shortpage channel time slot 628 to determine whether there may be a telephonecall or paging message directed to the mobile station 106.

To detect the potential presence of a telephone call or paging message,the mobile station 106 combines the 39 coded bits 604 and the 39 codedbits 608 into a stream of 78 coded bits 614. Using known techniques, themobile station 106: (1) reorders the 78 coded bits if they wereinterleaved; (2) decodes the 78 coded bits to reverse the convolutionalcoding performed prior to transmission of the short page channel timeslot to derive 39 bits 616; (3) verifies the correct receipt of 25 bitsof identity information 622 by examining a 10-bit cyclic redundancycheck (CRC) 618 placed in the time slot by the mobile switching center102 during generation of the short page channel information; and (4)uses four zero bits 620 to reset a decoder. The 25 bits include four6-bit fields that may contain mobile station identity values 624 and onereserved bit 626.

Each of the four six-bit fields may contain an identity valuecorresponding to one or more mobile stations 106. To scan for telephonecalls or paging messages, each mobile station 106 examines apredetermined, six-bit field to check for a short page identity match(described in more detail below). More than one mobile station 106 mayexamine the same six-bit field, and more than one mobile station 106 mayderive a short page identity match and be alerted to a possibletelephone call. Each alerted mobile station 106 then examines standardpaging channel (PCH) information according to standard GSMspecifications to determine whether the telephone call or paging messageis intended for the respective mobile station 106. If not, the mobilestation 106 resumes scanning of short page channels (SPCH).

In one embodiment of the present invention, the mobile station 106examines one of four 6-bit mobile station identity values 624 todetermine whether a telephone call or paging message was directed to themobile station 106. Those of ordinary skill in the art will appreciatethat six bits may not uniquely identify a mobile station from othermobile stations 106 simultaneously using a GSM network. It will beappreciated, however, that because each short page channel contains fourtime slots and because each time slot contains four 6-bit values 624,only one out of every 16 mobile stations may be examining the same 6-bitvalue. This is because each mobile station 106 may be assigned one ofthe four time slots of a short page channel 504 and may further beassigned one of the four 6-bit values 624 within the assigned time slot.It will further be understood that the range of a 6-bit value (0-63) issufficient to identify 64 different mobile stations 106. The embodimentillustrated in FIG. 6 thus suffices to uniquely identify any one of 64different mobile stations 106 within any one of 16 different groups ofmobile stations 106. In other words, the embodiment illustrated in FIG.6 can uniquely alert one out of each 1,024 mobile stations 106 of apending telephone call or paging message.

One of ordinary skill in the art will appreciate that the 25 bits ofidentity information 622 could be allocated differently. For example,three 8-bit fields may contain mobile station identifier values alongwith one reserved bit. As another example, six four-bit fields maycontain mobile station identifier values along with one reserved bit.Alternatively, the 24 bits could be allocated to a single mobile stationidentifier value, providing the ability to uniquely identify over 16million mobile stations 106. However, including four six-bit fields in asingle time slot 506 strikes an advantageous balance in providing for asufficient number of potential call alerts while, at the same time,minimizing the additional load on the physical control channel caused byintroducing another logical channel (the SPCH channel) and alsominimizing the number of false alerts.

In alternative embodiments of the present invention, short page timeslots may have fewer than or more than 25 bits of identity information.For example, one embodiment of a short page time slot includes only 26synchronization bits and an additional 38 coded bits. Thus, followingany interleave-required reordering and following decoding to reverseconvolutional coding, this embodiment provides 44 bits (25+19=44) ofidentity information. The 44 bits could be divided up many differentways to represent mobile station identifiers, such as five 8-bit fieldsfor mobile station identifiers and four reserved bits. However,regardless of how many bits are allocated to identity information, themobile station 106 need only receive, store and process the bit-orienteddata of a single time slot to be alerted to the possibility that atelephone call or paging message has been directed to the mobile station106.

According to existing GSM-based wireless communication systems, mobilestations receive, store and process four time slots of a paging channel(PCH) to determine whether a telephone call or paging message ispending. Under the present invention, a mobile station 106 in standbymode (waiting for a telephone call or paging message) need never processmore than a single time slot to detect the possibility that a telephonecall or paging message has been directed to the mobile station 106. Theamount of data in a short page (SPCH) time slot of the present inventionis only 25% of the amount of data in a four-time slot PCH, and the SPCHtime slot may be received in just 25% or less of the time periodrequired to receive the four-time slot PCH. Moreover, the SPCH time slotmay be processed by the mobile station 106 in around 25% of the timerequired to process a four-time slot PCH.

The reduced receiving time and processing time for an SPCH time slotdirectly reduces the battery power consumption of a mobile station 106in standby mode. The amount of battery power consumed by a mobilestation 106, for example, a cellular telephone, to receive and process asingle time slot of a short page channel (SPCH) is approximately 25% ofthe power consumed by the same mobile station 106 to receive and processfour time slots of standard paging channel (PCH) information. Thus, useof the short page channel SPCH may quadruple the standby mode lifetimeof a mobile station battery.

FIG. 7 illustrates components of a mobile switching center 702 accordingto one embodiment of the present invention. A software instructionprocessing unit 704 loads and processes executable software instructionsstored in a software instruction storage 706. The software instructionstorage 706 may be any computer-readable storage media, including aprogrammable read-only memory (PROM) device or a hard disk drive. Thesoftware instruction storage includes an SPCH registration module 714and an SPCH creation module 716. The software instruction processingunit 704 reads data values from and writes data values to a memory 708which may be any type of computer-readable memory which allows aninstruction processing unit to write and store data values into thememory. One such memory 708 is a standard hard disk. The memory 708includes a visitor location register 710 (VLR) which organizes andstores information identifying characteristics about particular mobilestations 106. The software instruction processing unit 704 executesinstructions of the SPCH registration module 714 to store information inthe VLR 710 including identity information and channel assignmentinformation for a mobile station 106. The memory 708 also includes oneor more channel buffers which store data received from mobile stations106 or which store data to be transmitted to mobile stations 106. Thesoftware instruction processing unit 704 executes instructions of theSPCH creation module to generate a short page channel SPCH fortransmission to mobile stations 106 via a base station 104.

FIG. 8 illustrates components of a mobile station 106 according to oneembodiment of the present invention. A software instruction processingunit 802 loads and executes instructions stored in a softwareinstruction storage 804. The software instruction storage 804 may be anytype of computer-readable medium such as a PROM or an erasable PROM(EPROM). The software instruction processing unit 802 reads data valuesfrom and stores data values to a memory 806 which may be any type ofcomputer-readable medium permitting a processor to write and store datavalues into the memory 806. A master clock 808 times the execution ofsoftware instructions by the software instruction processing unit 802.In one embodiment of a mobile station 106, a low accuracy (or lowprecision) clock 810 also times instructions executed by the softwareinstruction processing unit 802. The low accuracy (or low precision)clock is preferably one that consumes less power than the master clock808 ordinarily used. This may advantageously be accomplished by using aclock having a lower clock speed or a lower frequency than the masterclock 808. In such a case, it can be seen that the master clock 808 andits associated circuitry would do more processing and consume more powerthan the low accuracy clock 810. The low accuracy (or low precision)clock 810 may thus consume less power because it need not have thestability or resolution that the master clock needs. A battery 812provides power to components of the mobile station 106, including thesoftware instruction processing unit 802, the master clock 808, and thelow accuracy clock 812.

An SPCH data buffer 814 contains short page channel time slot datareceived by the mobile station 106. The software instruction processingunit 802 executes instruction of an SPCH receiving module 816 to controlthe receipt of short page channel time slot data transmitted by a basestation 104. The SPCH receiving module 816 is stored in the softwareinstruction storage 804. Also stored in the software instruction storage804 is an SPCH processing module 818. The software instructionprocessing unit 802 executes instructions of the SPCH processing module818 to process information in the SPCH data buffer 814 to detect callalerts.

Those of ordinary skill in the art will appreciate that instructions ofsoftware modules, such as the SPCH receive module and the SPCHprocessing module, may be combined into a single module. Moreover, itwill be appreciated that modules stored in the software instructionstorage 804, as illustrated in FIG. 8, are not exclusive, and that othermodules, particularly those existing in the art such as modules forreceiving and processing paging channels 218 PCH, may be stored inaddition to those illustrated in FIG. 8.

While battery power is conserved by minimizing the processing of pagingchannels PCH having four time slots each, battery power is furtherconserved by avoiding unnecessary processing of other logical channelssuch as the broadcast control channel 214 BCCH. The mobile station 106receives and processes the reserved bit 626 included in a short pagechannel SPCH time slot 506 to avoid redundant processing of a BCCHchannel.

In existing GSM systems, mobile stations in standby mode now monitorbroadcast control channels 214 (BCCH) in accordance with GSMspecifications to receive updated information, including possiblechanges in communication parameters. Currently, mobile stations monitora broadcast control channel (BCCH) at least once every 30 seconds, thusaccessing a BCCH in approximately one of every 120 multiframes.

In one embodiment of the present invention, when the mobile station 106receives a first short page channel (SPCH) time slot, the softwareinstruction processing unit 802 executes instructions of the broadcastcontrol channel (BCCH) update module 822 to store the value of thereserved bit in computer-readable memory, such as a flash memory, eitherinternal to the mobile station 106 or on a SIM card. When the mobilestation 106 receives the next short page channel (SPCH) time slot,instructions of the broadcast control channel update module 822 comparethe value of the newly received reserved bit to the value of the storedbit. The two values will differ when the content of the broadcastcontrol channel (BCCH) differs from a prior transmitted broadcastcontrol channel. The mobile station 106 need not scan for or process anybroadcast control channel until the content of the broadcast controlchannel changes. Eliminating the processing of redundant broadcastcontrol channels BCCH reduces processing requirements during standbymode operation and hence conserves battery power. In alternativeembodiments, more than one bit may be reserved for indicating to themobile station 106 that there is some reason to scan for and receiveparticular broadcast data.

Operation of One Embodiment of the Invention

In operation, in accordance with one embodiment of the invention, amobile station 106 is powered on inside a cell 108. The mobile station106 scans GSM frequencies to synchronize with the transmission from abase station 104. Once synchronization is established (a frequencycorrection channel 210 FCCH, a synchronization channel 212 SCCH, and abroadcast control channel 214 BCCH have been received and processed),the mobile station 106 registers with the mobile switching center 102associated with the cell in which the mobile station 106 is located.During registration, the mobile switching center 102 generates atemporary mobile subscriber identity (TMSI) and a short page identifier(SPI). These are recorded in a visitor location register (VLR) alongwith the cell location of the mobile station 106. The mobile switchingcenter 102 transmits the TMSI value and the SPI value to the mobilestation 106 which stores them and then transmits an acknowledgment ofits receipt of those values back to the mobile switching center 102. Themobile switching center 102 also assigns the mobile station 106 to acertain paging group and to a certain short paging group. The paginggroup value determines which portions of a base station 104 transmissionthe mobile station 106 will receive and process to detect telephonecalls or paging messages. Similarly, the short paging group numberdetermines which portions of a base station 104 transmission the mobilestation 106 will receive and process to detect call alerts. The mobileswitching center 102 transmits the paging group number and the shortpaging group number to the mobile station 106 which acknowledges itsreceipt of those values in a return message.

The mobile station 106, in a cell 108, then enters standby modeprocessing wherein it scans base station 104 transmissions for callalerts. The base station 104 transmits multiframes at the rate of oneapproximately every 0.25 seconds. The mobile switching center 102creates multiframes and includes a short page channel 504 in eachmultiframe 502. Each short page channel 504 SPCH advantageously has fourtime slots 506 (although a single time slot alerts a mobile user topotential telephone calls or paging messages). The mobile switchingcenter 102 sends each multiframe it creates to a base station 104 fortransmission in a cell 108.

Depending on the mobile station's 106 short paging group number, it willreceive and process a certain time slot of the short page channel 504 inselected multiframes 502. For example, the mobile station's 106 shortpaging group number may specify that the mobile station 106 may detectcall alerts by receiving and processing the second time slot of theshort page channel 504 of every second multiframe 502. Thus, because amultiframe 502 is transmitted every 0.25 seconds, the mobile station106, receiving a time slot from every second multiframe 502, detectspossible call alerts every 0.5 seconds.

FIG. 15 illustrates two sequences of multiframes, one sequence beingused by existing GSM-based systems having no short page channels 504SPCH, and another sequence in accordance with a preferred embodiment ofthe present invention using short page channels 504 SPCH. A firstsequence of multiframes illustrates the use of two paging channels 1508PCH in every other multiframe. Thus, a first multiframe 1502 includesfirst and second paging channels 1508. A second multiframe 1504,transmitted after the first multiframe 1502, includes no paging channelsfor the mobile station 106, but the second multiframe 1504 may includepaging channels for other mobile stations. A third multiframe 1506 againincludes first and second paging channels 1508. The first sequence ofmultiframes (illustrated by three consecutive multiframes 1502, 1504,1506) permits a mobile station 106, according to existing GSM standards,to receive and process a paging channel 1508 PCH every 0.5 seconds byreceiving and processing one full paging channel 1508 in every othermultiframe (each multiframe has a transmission duration of approximately0.25 seconds).

A second sequence of multiframes 1510, 1504, 1512 illustrates thetransmission of a short page channel 1514 in accordance with a preferredembodiment of the present invention. A multiframe 1510 includes oneshort page channel 1514 SPCH and one paging channel 1508 PCH. Anothermultiframe 1504, transmitted approximately 0.25 seconds after themultiframe 1510, includes no short page channels for the mobile station106 and includes no paging channels for the mobile station 106, but themultiframe 1504 may include short page channels and paging channels forother mobile stations. Another multiframe 1512, transmitted after themultiframe 1504, again includes one short page channel 1514 SPCH and onepaging channel 1508 PCH. The second sequence of multiframes 1510, 1504,1512 permits a mobile station 106 to receive and process one time slotof a short page channel 1514 SPCH every 0.5 seconds.

As another example, the mobile station's 106 short paging group numbermay specify that the mobile station 106 receives and processes a timeslot of a short page channel 504 once every eight multiframes 502. Inthat case, the mobile station 106 detects possible call alertsapproximately every two seconds.

Each time slot of a short page channel 504 includes four 6-bit mobilestation identifier values 624. The mobile station's 106 short paginggroup number also specifies which of the four 6-bit mobile stationidentifier values 624 the mobile station 106 should examine to detect acall alert. For example, a mobile station's 106 short paging groupnumber may specify that a mobile station 106 examines the third 6-bitmobile station identifier value 624 in a short page channel SPCH timeslot. Thus, to detect a call alert (to determine whether a telephonecall or paging message may have been directed to the mobile station106), the mobile station 106 compares the value of the third 6-bitmobile station identifier value 624 to the internally stored SPI value.If that compare operation results in a match, then the mobile station106 begins receiving and processing standard paging channels 218 todetermine if the mobile station 106 is the intended recipient of thetelephone call or paging message.

In accordance with the GSM standard, the mobile station 106 receives andprocesses standard paging channel 218 PCH information approximatelyevery 0.5 to 2 seconds. Just as with the short paging group number, amobile station's 106 paging group number determines the frequency atwhich the mobile station 106 will receive and process each page channel218 PCH and also which paging channel 218 PCH, of potentially many, in amultiframe 502 the mobile station 106 should access.

When the mobile station 106 receives a paging channel 218, it receivesfour time slots of information. To detect whether the mobile station 106was the intended recipient of a telephone call or paging message, themobile station 106 decodes the four time slots and compares a mobileidentity value 414 included in the four time slots to an internallystored value. If a match is detected, then the mobile station 106carries out the standard GSM call establishment procedures. If there isno match, then the mobile station 106 returns to standby mode processingwherein it scans short page channel 504 information for call alerts andadvantageously avoids consuming large amounts of battery power toreceive and process standard paging channels PCH.

While in standby mode processing, the mobile station 106 advantageouslyenters an idle state between the receipt and processing of a short pagechannel 504 SPCH time slot and shuts down the master clock. Because eachtime slot of a short page channel 504 SPCH includes 64 synchronizationbits, the short page channel 504 time slot may be easily locked onto(synchronized) and recognized. The synchronization bits thus reduce theprecision in timing needed to receive the short page channel 504 SPCHtime slot. Accordingly, a low precision clock is used to time the idlestate rather than the more precise master clock. Shutting down themaster clock in the idle state conserves battery power as the lowprecision clock consumes far less power than the master clock. When theidle state expires, the master clock is started and stabilized in timeto receive the next short page channel SPCH time slot.

Upon receiving each short page channel 504 SPCH time slot, the mobilestation 106 examines the value of a reserved bit included in the SPCHtime slot. The mobile station 106 compares the value of the newlyreceived reserved bit to the value of the reserved bit in theimmediately preceding short page channel 504 SPCH time slot, which bitthe mobile station 106 has stored in internal memory. When the reservedbits differ, there has been some change in the broadcast control channel214 BCCH information, and the mobile station 106 then receives andprocesses the four time slots of the next broadcast control channel 214.Thus, use of the reserved bit to identify changes in the broadcastcontrol channel information, allows the mobile station 106 to avoidreceiving and processing redundant, unnecessary broadcast controlchannels 214 and thus to avoid unnecessary consumption of battery power.The mobile switching center 102 makes this possible by comparing thecontent of each new broadcast control channel 214 to the content of theimmediately preceding broadcast control channel and adjusting thereserved bit in the short page channel 504 SPCH as necessary prior totransmission of the SPCH in a cell 108. Aspects of the foregoingoperation description are discussed in more detail below.

FIG. 9 illustrates steps performed by a mobile station 106 to registerwith a mobile switching center 102. In a first step 902, the mobilestation 106 (e.g., a cellular telephone) is powered on. Next, in a step904, the mobile station 106 scans radio broadcast frequencies used by aGSM-based wireless communication system. In a further step 906, themobile station 106 synchronizes to the GSM network. Using knownsynchronization steps, the mobile station 106 first synchronizes to afrequency by scanning for a physical channel having the highest apparentpower level. The mobile station 106, having located such a physicalchannel, searches for a frequency correction channel (FCCH) signalconsisting of a sequence of zero-valued bits filling an entire time slotof the channel. The FCCH signal is a logical channel mapped to the firsttime slot of a data frame. As illustrated in FIG. 5, there may be fiveFCCH logical channels (each identified in FIG. 5 by “F”) in a multiframe502.

After locating a frequency correction channel FCCH, the mobile station106 synchronizes timing by scanning for a synchronization channel (SCH)from which it obtains timing information such as, for example, a currentframe number. Each SCH is a logical channel mapped to the first timeslot of a data frame. As illustrated in FIG. 5, there may be five SCHlogical channels (each indicated by an “S” in FIG. 5) in a multiframe502. According to GSM specifications, the mobile station 106 alsosynchronizes to a base station 104 by scanning for a broadcast controlchannel (BCCH) to obtain information such as the location for the cell108, cell options, as well as information on how to communicate with thebase station 104. In still a further step 908, the mobile station 106registers with the mobile switching center 102.

FIG. 10 illustrates steps performed by a mobile station 106 and a mobileswitching center 102 to register and activate the mobile station 106 ina cell 108. In a first step 1002, the mobile station 106 requests acommunication channel. In a next step 1004, the mobile switching center102 assigns a channel for the mobile station 106 to use in completingthe registration procedure. (See, for example, Siegmund M. Redl, et al.,An Introduction to GSM, 40 (1995) which is hereby incorporated byreference herein in its entirety). In a further step 1006, the mobilestation 106 requests a location update.

In a step 1008, the mobile switching center 102 stores the mobilestation's 106 telephone number as well as the mobile station's 106international mobile subscriber identity (IMSI) in a computer-readablestorage area called a visitor location register (VLR). Those of ordinaryskill in the art will appreciate that the IMSI number is a 60-bit valuewhich uniquely identifies a mobile station and that, typically, the IMSIis stored on a subscriber identity module (SIM). A SIM is a smart cardhaving computer-readable memory, the SIM card being inserted into amobile station prior to the mobile station 106 being used in a cell. Ina further step 1010, the mobile switching center 102 accepts and storesin the VLR the mobile station's 106 cell location.

In a step 1012, the mobile switching center 102 generates a 32-bittemporary mobile subscriber identity (TMSI) value. The TMSI is assignedto the mobile station 106 and used to identify the mobile station 106while it is using the GSM network. The mobile switching center 102stores the TMSI value in the VLR and transmits the TMSI value to themobile station 106. The mobile station 106 acknowledges its receipt ofthe TMSI in a message it transmits back to the mobile switching center102.

In one embodiment of the present invention, in a step 1014, instructionsof the SPCH registration module 714 as executed by the softwareinstruction processing unit 704 generate a 6-bit short page identity(SPI) value. The SPI may represent 6 bits from the TMSI value, or 6 bitsfrom the IMSI value. Alternatively, the 6 bits may represent sometransformation, such as a hash function combined with a modulooperation, performed on the TMSI or IMSI value. In still anotherembodiment, the 6 bits of the SPI may be selected by instructions of theSPCH registration module 714 completely independent of the TMSI and IMSIvalues for a mobile station 106, such as by incrementing a 6-bit counterand associating the resulting value with a registering mobile station106 (setting the counter to 0 when incrementing the binary counter value111111). In the step 1014, instructions of the SPCH registration module714 associate the selected 6-bit SPI value with the mobile station 106by storing the 6-bit SPI value in the VLR. It will be appreciated thatif the 6-bit SPI value is generated based on some portion ortransformation of the mobile station's 106 IMSI or TMSI number, then the6-bit SPI need not be stored in the VLR and can be computed by themobile switching center 102 or the mobile station 106 whenever needed.

In another step 1015, the mobile switching center 102 transmits to themobile station 106 the selected 6-bit short page identity. The mobilestation 106 stores the 6-bit short page identity value in acomputer-readable memory, such as a flash memory, located either in themobile station or in the SIM. In the step 1015, the mobile station 106transmits a message to the mobile switching center acknowledging receiptof the 6-bit SPI value. In an alternative embodiment, wherein the 6-bitvalue is calculated based on some transformation of either the TMSI orIMSI, then the 6-bit value need not be communicated from the mobileswitching center 102 to the mobile station 106.

In a further step 1016, the mobile switching center 102 associates themobile station 106 with a paging group number according to known GSMspecifications. The selected paging group number relates to a particularpaging channel 218 (PCH) in a multiframe 208. Generally, existing mobilestations examine a paging channel (PCH) every 0.5 to 2 seconds. A51-frame multiframe is transmitted approximately every 0.25 seconds.Thus, a typical mobile station skips from one to seven multiframesbetween processing of a page channel (PCH). The paging group numberdetermines how many multiframes a mobile station 106 skips betweenprocessing paging channels.

The mobile station 106, once associated with a particular paging groupnumber, uses known GSM specifications to scan for telephone calls orpaging messages directed to the mobile station 106 by receiving andprocessing just the paging channel information identified by the paginggroup number. For example, if a mobile station 106 is associated with apaging group number which relates to the first paging channel 218 (PCH)(see FIG. 2) occupying time slots 7-10 in a 51-frame multiframe, thenany telephone calls or paging messages directed to the mobile station106 would be represented in the four time slots of the first pagingchannel in the multiframe, and the mobile station 106 may disregardother common control channels without any risk of missing telephonecalls or paging messages.

Those of ordinary skill in the art will also appreciate that a paginggroup number, under the GSM specification, may identify a single pagingchannel (PCH) in a span of up to 8 multiframes. In such a case, themobile station 106 need only examine one particular paging channelwithin 8 entire multiframes to determine whether any telephone call orpaging message has been directed to the mobile station 106. Also, inaccordance with standard GSM practices, a mobile station 106 cancalculate a paging group number by accessing a channel distributionvalue from a broadcast control channel (BCCH) and performing apredetermined calculation using the channel distribution value.

In an embodiment of the present invention, instructions of the SPCHregistration module 714, in a step 1018, associate the mobile station106 with a short paging group number. In one embodiment, the shortpaging group number relates to a specific short page channel (SPCH) 504(see FIG. 5) within one of up to eight multiframes 502. Further, theshort paging group number refers to one of the four time slots 506 in ashort page channel (SPCH) 504 and also identifies one of four possible6-bit mobile station identifiers 624 (see FIG. 6) carried in a singletime slot of a short page channel. Thus, using the short paging groupnumber in accordance with the present invention, the mobile station 106understands which multiframes to access, which short page channel SPCHto access, which time slot of the SPCH to access, and which 6-bit mobilestation identifier value to access in order to detect call alerts.Alternatively, rather than specifying which time slot (1-4) of a shortpage channel SPCH to access, the short paging group number could specifywhich time slot (1-51) of a multiframe to access.

In another alternative embodiment wherein the mapping of signal channelInformation across a multiframe is changed and wherein short pagechannel SPCH time slots are not located in four successive time slots,the short paging group number could reference a particular time slot ina multiframe, or a particular time slot from a number of multiframes.For example, the short paging group number may reference the seventhtime slot of every other multiframe, the 17th time slot of every thirdmultiframe, or the 33rd time slot of every sixth multiframe. Moreover,in various embodiments, a single time slot of a short page channel maycontain one, two, three, or more mobile station identifier values havingbit lengths other than 6 bits. In any of those various embodiments, theshort paging group number may reference one of the mobile stationidentifiers contained in a time slot of a short page channel (SPCH). Forexample, a 12-bit short paging group number could be allocated asfollows: 2 bits (a value ranging from 0-3) to identify one of four 6-bitmobile station identifiers 624 contained in a single short page channel(SPCH) time slot, 6 bits (a value ranging from 0-63) to identify asingle time slot (1-51) in a 51-frame multiframe, and 4 bits (a valueranging from 0-7) to identify a span of up to 8 multiframes.

In one embodiment of the present invention, a mobile station 106extracts a channel distribution value from a broadcast control channel(BCCH) and uses the channel distribution value to calculate a shortpaging group number. Alternatively, the mobile switching center 102transmits the short paging group number to the mobile station 106whereupon the mobile station 106 stores the short paging group number incomputer-readable memory, such as flash memory, either internal to themobile station 106 or on a SIM card. A mobile switching center 102selects a short paging group number for the mobile station 106 tobalance short page signaling information across each multiframetransmitted to a cell 108.

After registering with the network, the mobile station 106 can then usethe network to initiate or receive telephone calls or page messages. Inone embodiment of the present invention, the mobile station 106 reducesthe processing associated with standby mode (scanning for pendingtelephone calls or page messages) by examining fewer paging channels(PCH) in a time period than the number recommended or directed by themobile switching center 102. For example, the mobile switching center102 determines that the mobile station 106 belongs to a paging groupwhich examines a paging channel 218 (PCH) occupying time slots 7-10 of a51-frame multiframe 208, and the paging group only examines every secondmultiframe (i.e., skips 1 multiframe between processing of theidentified paging channel 218). Existing mobile stations would respondby processing the identified paging channel 218 in every secondmultiframe. According to one embodiment of the present invention, themobile station 106, having been directed by the mobile switching center102 to process the paging channel 218 in every second multiframe,instead doubles the multiframe skipping value and examines the pagingchannel 218 in every fourth multiframe.

In this embodiment, the mobile station 106 conserves battery power byreducing the amount of processing associated with standby mode (scanningfor telephone calls or paging messages). Because the mobile switchingcenter 102, under the current GSM standard, will broadcast pagingchannel information about four times for a particular paging group, themobile station 106 is not likely to miss a call. Further, the systemcould be modified slightly to increase the number of times the paginginformation is sent. However, because the standby processing time and,hence, power consumption is cut roughly in half, the lifetime of themobile station's 106 battery 812 is approximately doubled. Just aspaging channel (PCH) information may be skipped to conserve batterypower, short page channel (SPCH) information may also be skipped.

A short paging group number, discussed in more detail below, may directa mobile station 106 to examine and process particular short pagechannels (SPCH) from particular multiframes. For example, a short paginggroup number may direct a mobile station to process the first time slot628 of the first short page channel 504 (SPCH) of every 4th multiframe502. The mobile station 106 may respond to such direction by processingthe first time slot 628 of the first short page channel 504 (SPCH) ofevery 8th multiframe 502. In this manner, the mobile station 106 reducesthe amount of battery power consumed during standby mode. Because theamount of short page channel information is cut roughly in half, thebattery power consumption applied to monitoring the short page channelis also cut in half. Any risk of missing a short page channel may beavoided in an embodiment wherein the mobile switching center increasesthe number of short pages for a pending telephone call or paging messageto compensate for the skipping, providing the same exposure to the shortpage channel as the mobile station 106 would have if it skipped no shortpage channels. Increasing the number of short pages could be donedynamically, such as whenever the mobile switching center determinesthat increasing the number of short pages for a telephone call or pagingmessage would not substantially affect the load on a time slot (physicalchannel).

FIG. 11 illustrates steps performed in one embodiment of the presentinvention to scan a base station 104 transmission for telephone calls orpage messages. In a first step 1102, the mobile station 106 receives andprocesses information in the broadcast channel 214 to extract a channeldistribution value. In a next step 1104, the mobile station 106calculates a short paging group number using the channel distributionvalue. In one embodiment, the short page channel distribution valueindicates two quantities: (1) the number of multiframes for the nextshort page channel (this value can be designated M); and (2) the numberof short paging frames in a 51-frame multiframe (this value can bedesignated N). The software instruction processing module advantageouslyexecutes instructions of the short paging group number calculationmodule 820 to perform a modulo 4 operation (remainder of division by 4)on the mobile station's 106 IMSI number to derive a 2-bit value (0, 1,2, or 3) representing which of four possible 6-bit mobile stationidentity values 624 the mobile station 106 may examine. The short paginggroup number calculation module 820 then advantageously derives a 6-bitvalue by performing a modulo N (remainder of division by N) operation onthe mobile station's 106 IMSI number to identify a particular time slotwithin a multiframe. The short paging group number calculation modulealso advantageously performs a modulo M operation on the mobilestation's 106 IMSI number to derive a 4-bit number (0-7) representing anumber of multiframes between those multiframes having short pagechannel information for the mobile station 106 (e.g., the value 5indicates that the mobile station 106 should skip 5 multiframes beforeexamining another short page channel, in other words to examine shortpage channel information in every 6th multiframe). Thus, the shortpaging group number indicates to the mobile station 106 whichmultiframes to examine for short page channel information, which timeslot in a multiframe to examine, and which mobile station identity valueto examine within a selected time slot.

In a step 1106, the mobile station 106 enters an idle state wherein itperforms no processing until the next transmission of the short pagetime slot referenced (and determined) by the short paging group number.In such idle state, the mobile station's 106 use of battery power isminimized. In a further step 1108, the mobile station 106 becomes activeand the software instruction processing unit 802 executes instructionsof the SPCH receive module 816 to receive and store bit data from theshort page channel (SPCH) time slot identified by the short paging groupnumber.

In a step 1110, the software instruction processing unit 802 executesinstructions of the SPCH processing module 818 to enable the mobilestation 106 to process the bit data from the short page channel timeslot. Accordingly, in the step 1110, the mobile station 106 drops thetail bits 602, 610, the synchronization bits 606, and the guard periodbits 612, and combines the first 39 coded bits 604 and the second 39coded bits 608 into a stream of 78 coded bits 614. In an alternativeembodiment wherein the 78 bits are interleaved, the mobile station 106reorders the 78 bits. In a further step 1112, the mobile station 106decodes the coded bits to reverse convolutional coding.

In a further step 1114, the mobile station 106 advantageously uses a10-bit cyclic redundancy check 618 to verify accuracy of the bits. Next,in a step 1116, the mobile station 106 extracts one of four possible6-bit mobile station identifiers 624 carried by the short page timeslot. The mobile station 106, still executing instructions of the SPCHprocessing module 818, determines which 6-bit mobile station identifierto extract by examining the short paging group number (which it eithercalculates or which has already been stored in the mobile station's 106memory) which references one of the four 6-bit mobile stationidentifiers 624.

In a step 1118, the mobile station 106 compares the extracted 6-bitmobile station identifier to a 6-bit identifier value stored in flashmemory in either the mobile station itself or in the SIM card. If, inthe step 1120, the mobile station 106 determines that the two 6-bitvalues match, then the mobile station 106 is alerted that there may be atelephone call or page message directed to the mobile station 106, inwhich case the mobile station 106, in a step 1122, performs steps toreceive and process the next paging channel (PCH) signal. If, however,in the step 1120, the mobile station 106 determines that the extracted6-bit mobile station identifier value does not match the internallystored 6-bit identifier value, then processing loops back to the step1106 wherein the mobile station 106 enters an idle state until the nexttransmission of the short page channel (SPCH) time slot.

Once a mobile station 106 is alerted in accordance with the presentinvention to the presence of a telephone call or paging messagepotentially directed to the mobile station 106, then the mobile station106, in one embodiment of the present invention, carries out certainsteps already practiced in the art to access and examine paging channel(PCH) information to determine with certainty whether it is the intendedrecipient of the telephone call or paging message. Because of the lengthof the alert message, 6 bits in one embodiment, the mobile stationcannot always be uniquely identified, that is, the same 6-bit code maybe assigned to more than one mobile station. Occasional false alerts donot detract from the value of the present invention because the shortpage message still results in significant power consumption savingsduring the standby period.

Following each alert, the mobile station 106 examines an appropriatefour-time slot paging channel (PCH) 218 (see FIGS. 2 and 5) to ascertainif the mobile station 106 is the intended recipient of the telephonecall or page message. The total power consumption associated withexamining single short page time slots for call alerts and occasionalprocessing of paging channel (PCH) information associated with falsealerts is far less than the power consumption associated with repetitiveprocessing of four-time slot paging channels (PCH) to determine in everypossible case whether the mobile station 106 is the intended recipientof a phone call or page message.

FIG. 12 illustrates steps performed by a mobile station 106 to determinewhether it is the target of a pending telephone call or page message.Some of the steps in FIG. 12 would be practiced in existing systems notusing the present invention. In a first step 1202, the mobile station106 receives and processes information in the broadcast channel (BCCH)to extract a channel distribution value. In a further step 1204, themobile station 106 calculates a paging group number using the channeldistribution value. The paging group number identifies a particularpaging channel PCH the mobile station 106 should examine to determinewhether any telephone calls or page messages have been directed to themobile station 106.

In a further step 1208, the mobile station 106 receives and storespaging channel (PCH) bit data from the four time slots of the pagingchannel (PCH). Using known GSM-based techniques, the mobile station 106reorders interleaved bit data in a step 1210 and, in another step 1212,decodes the bit data to reverse the convolutional coding performed priorto transmission of the paging channel (PCH) data.

In still another step 1214, the mobile station 106 extracts mobilestation identifier bits from the decoded bit data. In a further step1216, the mobile station 106 compares the extracted mobile stationidentifier bits to a mobile station ID code stored internally incomputer-readable memory, such as a flash memory in the mobile station106 or in a SIM card. If, in a step 1218, the mobile station 106determines that the extracted mobile station identifier bits match theinternally stored mobile station identifier, then, in a step 1220, themobile station 106 initiates call establishment procedures. Those ofordinary skill in the art will have familiarity with GSM-based callestablishment procedures. If, however, in the step 1218, the mobilestation 106 determines that there is no match, then the mobile stationenters an idle state in accordance with one embodiment of the presentinvention described in relation to step 1106 (see FIG. 11) to await thenext transmission of a short page channel (SPCH) time slot.

Some embodiments of the present invention advantageously ensure backwardcompatibility with mobile stations that cannot process short pagechannel (SPCH) information. In those embodiments, the mobile switchingcenter 102 generates standard paging channels (PCH) and short pagechannels (SPCH) and transmits those channels to the base station 104 forre-transmission to the mobile stations 106. Thus, mobile stations 106not equipped to receive and process short page channel (SPCH)information may still rely on the presence of standard paging channel(PCH) information to detect telephone calls and page messages.Accordingly, some embodiments of the present invention are completelybackward compatible with existing implementations of the GSM standard inwireless communication networks, but also support mobile stations 106equipped to receive and process short page channels (SPCH).

FIGS. 13A and 13B illustrate steps performed by the mobile switchingcenter 102 to generate a short page channel (SPCH). In a first step 1302(see FIG. 13A), the mobile switching center 102 receives a call requestfrom a telephone user directed to a mobile station 106. In oneembodiment, the steps illustrated in FIGS. 13A and 13B following thestep 1302 are performed by instructions of the SPCH creation module asexecuted by the software instruction processing unit 704.

In a step 1304, the mobile switching center uses the phone number of thecall request as an index into the visitor location register (VLR) tolocate information related to the target mobile station 106. Inparticular, the mobile switching center 102 uses the phone number toobtain the mobile station's 106 TMSI value, the mobile station's 106short paging group number assignment, the mobile station's celllocation, and the mobile station's 6-bit identifier. As noted above, inalternative embodiments, the mobile switching center 102 calculates themobile station's 106 6-bit identifier from the mobile station's 106 TMSIor IMSI as necessary, and need not, in those embodiments, retrieve the6-bit value from storage.

The mobile switching center 102, in a step 1306, begins to generateshort page data to alert the mobile station 106 by filling a 6-bit valueusing the 6-bit identifier associated with the mobile station 106. Inanother step 1308, the mobile switching center 102 combines the 6-bitvalue with three other 6-bit values (either dummy values containingdummy bits or operative 6-bit values associated with other mobilestations to be alerted) and one reserved bit to form 25 short pageinformation bits. In one embodiment, the value of the reserved bitdepends on whether the content of the broadcast control channel haschanged. In this embodiment, instructions of the SPCH creation module716 compare the contents of a most recent broadcast control channel(BCCH) to the contents of the prior BCCH. If the contents differ, thenthe SPCH creation module toggles the value of the reserved bit,otherwise the value of the reserved bit is unchanged.

The mobile switching center 102 computes a 10-bit cyclic redundancycheck (CRC) and adds the 10-bit CRC value to the 25 short pageinformation bits, resulting in 35 bits. Next, in a step 1312, the mobileswitching center 102 adds four zero bits to the 35 bits for a total of39 bits. In a further step 1314 (see FIG. 13B), the mobile switchingcenter 102 performs convolutional coding on the 39 bits, facilitatingerror detection and correction by a receiving mobile station.Convolutional coding is well known in the art and is not described indetail herein. The convolutional coding doubles the number of bits,resulting in 78 coded bits. In a further step 1316, the mobile switchingcenter 102 divides the 78 coded bits into two 39-bit groups and places a64-bit synchronization sequence between the two 39-bit groups, creatinga 142-bit stream. The long, 64-bit synchronization sequence assists themobile station 106 in synchronizing with a time slot of the short pagechannel (SPCH) when it is ultimately transmitted by the base station104.

The mobile switching center 102 adds three tail bits at the beginning ofthe 142-bit stream and adds an additional three tail bits at the end ofthe 142-bit stream, creating a 148-bit stream. In a still further step1320, the mobile switching center 102 appends the 148-bit stream with an8.25-bit guard period, resulting in 156.25 bits.

The mobile switching center 102 then determines which of four time slotsin the short page channel has been assigned to the targeted mobilestation 106, and fills the assigned short page time slot with the 156.25bits. In a step 1324, the mobile switching center 102 combines thefilled short page time slot with three other short page time slots(possibly dummy time slots filled with dummy bits, or operational timeslots carrying bit-oriented data to alert other mobile stations) tocreate a full short page channel (SPCH). The mobile switching center 102next creates a multiframe in a step 1326 by combining the full shortpage channel (SPCH) with frequency correction channel (FCCH)information, synchronization channel (SCH) information, broadcastcontrol channel (BCCH) information, and common control channel (CCCH)information according to a predetermined multiframe mapping such as thatillustrated by FIG. 5. In a step 1328, the mobile switching center 102queues the newly created multiframe for transmission to the base station104. Upon receiving the multiframe, the base station 104 transmits themultiframe to the cell 108 containing the target mobile station 106.

As described above, in one embodiment of the present invention, themobile switching center 102 places a 64-bit synchronization sequencewithin the 156.25 bits of a short page channel (SPCH) time slot. Thoseof ordinary skill in the art will appreciate that such a format for bitsof a time slot is referred to as a synchronization burst 628 (SB) (seeFIG. 6). A short page channel time slot having fewer or more than 64synchronization bits may still carry sufficient short page informationbits to identify a mobile station 106 and to thereby alert the mobilestation 106 to a telephone call or page message. However, using thesynchronization burst format for a single short page channel time slotadvantageously reduces the timing precision needed by the mobile station106 to lock onto (synchronize with) a particular short page channel timeslot.

Typically, after a mobile station examines paging channel (PCH)information and determines that no telephone call or page message hasbeen directed to the mobile station 106, it enters a timed idle state.The mobile station 106 knows when the next paging channel (PCH)information will be transmitted, and the idle state period is preciselytimed so that the mobile station 106 will emerge from (exit) the idlestate just in time to receive the next paging channel (PCH). Existingmobile stations 106 use a highly precise master clock 808 to time theidle state with the necessary precision. One example of such a clock isa crystal-based clock operating at 13 MHz consuming approximately 2-3milliamps. Thus, even in the idle state, a mobile station 106 consumesbattery power to operate the master clock 808.

Lower accuracy (or lower precision) clocks 810 exist which consume farless battery power than the master clocks 808 typically used by mobilestations 106. One example of a lower precision clock is a clockoperating at 32 kHz consuming a few microamps. Because the relativelylong, 64-bit sequence of synchronization bits in one embodiment of theshort page channel time slot reduces the precision needed to time theidle state, a mobile station 106 in accordance with one embodiment ofthe present invention advantageously uses a low precision clock 810,rather than a highly precise master clock 808, to time the idle state,dramatically reducing battery consumption during the idle state.

FIG. 14 illustrates steps performed by a mobile station 106 inaccordance with one embodiment of the present invention to time an idlestate using a low precision clock 810. In a first step 1402, the mobilestation 106 detects no telephone calls or page messages by examiningeither a single time slot of a short page channel SPCH or four timeslots of a paging channel (PCH). In a further step 1404, the mobilestation 106 sets a timer based on a low precision clock 810. In anotherstep 1406, the mobile station 106 shuts down the master clock 808 andrelated circuitry, eliminating any battery power consumption by themaster clock 808. In one embodiment of the present invention, the lowprecision clock 810 is accurate to about 9 microseconds per second or 1second per day after calibration by the master clock 808.

With the timer set, the mobile station idles in a step 1408. Whileidling, the mobile station 106 need not consume any power beyond thatrequired to operate the low precision clock 810. The mobile station 106idles until the timer expires. In a further step 1410, the mobilestation starts and stabilizes the master clock 808. In one embodiment ofthe present invention the low precision clock 810 runs continuously. Inan alternative embodiment, the low precision clock 810 can be stoppedafter starting the master clock 808, and the low precision clock 810 canbe started just before stopping the master clock 808.

In another step 1412, the mobile station 106 starts receiver blocks. Thereceiver blocks perform the signal processing function of locking onto(synchronizing with) the next transmission of a short page channel(SPCH) time slot. It will be appreciated by those of ordinary skill thatexisting receiver blocks easily synchronize with a transmitted time slothaving a 64-bit synchronization sequence even when the synchronizationis timed with a low precision clock 810 accurate to 9 microseconds persecond or 1 second per day when calibrated by the master clock 808. In astep 1414, the mobile station 106 enters a receive state in which itreceives the next short page channel (SPCH) time slot to detect whethera telephone call or page message has been directed to the mobile station106.

In another embodiment, a clock having multiple precision levels is usedto time the idle state. During the idle state, before receipt of a nextshort page channel time slot, the clock is set to a lower precisionlevel, in which level the clock consumes less power than that consumedwhen the clock is operating at a higher precision level. At the end ofthe idle state, the clock is set to a higher precision level.

This invention may be embodied in other specific forms without departingfrom the essential characteristics as described herein. The embodimentsdescribed above are to be considered in all respects as illustrativeonly and not restrictive in any manner. The scope of the invention isindicated by the following claims rather than by the foregoingdescription.

What is claimed is:
 1. A method of operating a mobile station having asoftware instruction processing unit and a software instruction storagecomprising a computer-readable medium, comprising: scanning broadcastinformation in a wireless communication network for a short pagechannel; receiving a single time slot of said short page channelcontaining one group of call alert data, said wireless communicationnetwork operating in accordance with the GSM standard, said single timeslot being less than one millisecond in duration and representing lessthan 128 data bits; and processing said one group of call alert data anddetermining from said group of call alert data whether a pendingtelephone call or paging message may have been directed to the mobilestation.
 2. The method of claim 1, further comprising: entering an idlestate during a time period between broadcasts of said short pagechannel, in said idle state the mobile station does not scan for a shortpage channel or receive or process call alert information; consumingpower at a first rate during said scanning for said short page channeland during receiving or processing said call alert information; andconsuming power at a second rate in said idle state, said second ratebeing less than said first rate.
 3. The method of claim 2, furthercomprising: providing a master clock and a low precision clock, said lowprecision clock less precise than said master clock; timing the receiptof a single short page channel time slot using said low precision clock,said low precision clock consuming less power during a time intervalthan said master clock; timing said idle state using said low precisionclock; and shutting down said master clock during said idle state.
 4. Amethod of operating a mobile station, comprising: receiving a short pagechannel transmitted by a wireless communication system operating inaccordance with the GSM standard; extracting paging data from a timeslot of said short page channel; determining from said paging data insaid time slot that a telephone call or paging message may have beendirected to said mobile station, said time slot being less than onemillisecond in duration and representing less than 128 bits; andreceiving four time slots of a paging channel and responsivelydetermining whether the mobile station is an intended recipient of atelephone call or paging message.
 5. The method of claim 4, furthercomprising establishing a communication link to a communication deviceresponsible for initiating said telephone call or paging message.
 6. Themethod of claim 5, further comprising comparing a mobile stationidentity value to a short page identity value to make said determinationthat said telephone call or paging message may have been directed tosaid mobile station.
 7. A method of reducing requirements for processingbroadcast control data in a mobile station, comprising: receiving a bitof a time slot of a TDMA frame; storing said bit in a data storage area,said bit being reserved for updating broadcast control information;comparing said bit to a prior received bit stored in said data storagearea and, if said compared bits differ, directing the mobile station toreceive and process a next transmitted broadcast control channel toupdate communication parameters of the mobile station; and storing thenewly received bit in place of the prior received bit.
 8. A method ofoperating a wireless communication system, comprising: generating in amobile switching center a first single time slot of a short pagechannel, said first single time slot including a first mobile stationidentifier value; transmitting said first single time slot from saidmobile switching center to a base station; generating in said mobileswitching center a paging channel having four time slots, said four timeslots including a second mobile station identifier; transmitting saidfour time slots from said mobile switching center to said base station;receiving in a base station said first single time slot and said fourtime slots; transmitting said first single time slot in a short pagechannel and said four time slots in a paging channel from said basestation to a cell; receiving in said cell with a mobile stationidentified by said first mobile station identifier and said secondmobile station identifier, said first single time slot from said shortpage channel; extracting said first mobile station identifier from saidfirst single time slot to determine that a pending telephone call orpaging message may be directed to said mobile station; receiving withsaid mobile station, upon said determination, said four time slots fromsaid paging channel; extracting said second mobile station identifier toconclude that said mobile station is the intended recipient of saidtelephone call or paging message; and initiating in said mobile station,upon said conclusion, call establishment procedures to create acommunication link between said mobile station and a communicationdevice responsible for initiating said telephone call or paging message.9. The method of claim 8, further comprising: including in said firstsingle time slot a broadcast control update bit having a first value ifthe content of a most recently transmitted broadcast control channel insaid cell did not change from the content of an immediately precedingbroadcast control channel transmitted in said cell, said bit having asecond value if the content of the said recently transmitted broadcastcontrol channel is different from the content of said immediatelypreceding broadcast control channel; and extracting with said mobilestation said update bit from said first single time slot and, if saidupdate bit has said second value, then said mobile station receiving andprocessing a next transmitted broadcast control channel.
 10. The methodof claim 8, further comprising: storing a paging group value in a datastorage area, said paging group value specifying first paging channelsand being assigned to said mobile station by a mobile switching center;and storing a paging channel skipping value in said data storage area,said paging channel skipping value specifying a subset of said firstpaging channels, said subset identifying paging channels transmittedless frequently than said first paging channels, said mobile stationreceiving and processing said subset of said first paging channels. 11.The method of claim 10, further comprising: timing said receipt of saidfour time slots by said mobile station using a master clock;transmitting a second single time slot to said base station;transmitting from said base station to said cell said second single timeslot in said short page channel, said mobile station receiving saidsecond single time slot from said short page channel upon determiningfrom said receipt of said first single time slot that a pendingtelephone call or paging message is not directed to said mobile station;timing with a low precision clock the duration of an idle state whereinsaid mobile station does not receive, transmit, or process data, saidduration of said idle state occurring after said receipt by said mobilestation of said first single time slot and before said receipt by saidmobile station of said second single time slot, said second single timeslot containing sufficient synchronization bits to permit said receiptof said second single time slot; and shutting said master clock downduring said idle state, said low precision clock consuming less powerduring a time interval than said master clock.